Deformable Fastening Thread Providing Wedge-Effect

ABSTRACT

Disclosed is a fastener that includes a thread having a groove formed therein to provide a loosening resistance due to a deformation of the thread, the deformation resulting from a threshold axial force applied to the thread by a receiving structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/264,742, filed Sep. 14, 2016, entitled “Deformable Fastening ThreadProviding Wedge-Effect” and which the aforementioned application isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to fastening mechanisms, andmore particularly to a deformable fastening thread for increasing aloosening resistance of a threaded fastening arrangement.

BACKGROUND OF THE INVENTION

It is common for fastening elements such as bolts and nuts to befastened to one another, or to hold down one material to another. A boltmay have an external helical thread and a nut may have an internalhelical thread. The internal thread and the external thread may beconfigured to allow the nut and bolt to axially move relative to oneanother by torqueing one of the members relative to the other. Upontightening, the axial force between the nut and bolt is resisted by thethreads. As such, one or more materials may be sandwiched between a headof the bolt and the nut to tighten the nut and the bolt around the oneor more materials.

However, common fastening elements may loosen after being tightened. Forexample, thread profiles may be manufactured according to a certaintolerance, causing a tightened nut and bolt to loosen.

U.S. Pat. No. 8,671,547 issued to Matsubayashi et al. discloses afastening member that supposedly exerts a loosening-inhibition effect.However, Matsubayashi et al. is focused on elastic deformation of athread, and is therefore limited in providing a loosening resistance,since an elastic deformation of the thread would naturally be forcedback to an original undeformed state, which would cause or allowloosening axial forces.

Further, Matsubayashi et al. is focused on elastically deforming anexternal thread to directly increase a frictional force between aninternal flank of a nut and a pressure-side flank of an external thread,due to the elastic deformation. For example, an axial force resultingfrom a tightening torque applied to the screw of Matsubayashi et al.will be opposed and resisted by the elastic deformation. As such thehypothetical loosening-inhibition effect of Matsubayashi et al. iscaused by a loosening axial force directed away and opposite from atightening axial force direction.

The fastening arrangement proposed by Matsubayashi et al. is limited andproblematic in tightening two or more fastening members together, sincethe elastic deformation causes a loosening axial force (e.g. away from ahead of a bolt), opposing any fastening axial forces (e.g. toward a headof a bolt) which is normally required to tighten two objects together.For example, two pieces of material such as metal are commonly tightenedtogether by sandwiching the two materials between a head of a bolt orscrew, and a nut, and the elastic deformation of Matsubayashi et al.would resist tightening axial forces, thus defeating the purpose offastening arrangements of bolts or screws and nuts.

As such, there exists a need for a fastening thread for effectivelyincreasing a loosening resistance of a threaded fastening arrangement.

BRIEF SUMMARY OF THE INVENTION

Disclosed is a fastener comprising, a head end, and a helical threadhaving an insertion direction flank facing away from said head end and aremoval direction flank facing towards said head end, said removaldirection flank having a groove formed therein, said groove having amaximum depth being at least one half a thickness of said helical threadat a height position of said maximum depth of said groove on saidhelical thread.

In another aspect, said groove is disposed at a root of said thread.

In another aspect, said groove has a substantially triangularcross-section.

In another aspect, said groove has a curve in its cross section, saidcurve being between said height position of said groove and said removaldirection flank.

In another aspect, said groove is disposed substantially below a pitchdiameter of said thread.

In another aspect, said groove is configured to allow said thread todeform and increase a major diameter of said thread due to an axialforce.

In another aspect, said groove allows said thread to plastically deformdue to said axial force.

In another aspect, said groove allows said thread to plastically deformat a plastic hinge near said root of said thread.

In another aspect, said axial force is applied in response to atightening torque applied to said fastener.

In another aspect, due to said groove, said tightening torque transfersto cause a deformation of said thread to increase said major diameter ofsaid thread due to said deformation.

In another aspect, said maximum depth of said groove has a heightdimension that is at least half a distance between two roots of saidthread.

In another aspect, said axial force is applied in response to atightening torque applied to said fastener, said tightening torquecausing said fastener and a receiving structure to tighten together dueto said thread being helical.

In another aspect, due to said groove, said tightening torque transfersto cause a deformation of said thread to increase said major diameter ofsaid thread due to said deformation, said deformation being caused whena threshold axial force is applied to said removal direction flank.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows a side view of a fastener having a first embodiment of adeformable fastening thread;

FIG. 2 shows a deformation sequence of a partial view of the deformablefastening thread, the partial view taken from sectional line 2-2 of FIG.1;

FIG. 3 shows a second embodiment of a deformable fastening thread wherea groove of the thread is curved, in accordance with “FIG. 9” ofAppendix A;

FIG. 4 shows a conventional fastening thread engaging an internal threadof a nut, in accordance with “FIG. 7” of Appendix A;

FIG. 5 shows stress contours on the conventional fastening thread wherethe nut is applying an axial force to the conventional fastening thread,in accordance with “FIG. 11” of Appendix A; and

FIG. 6 shows stress contours on the second embodiment of the deformablefastening thread engaging an internal thread of a nut where the nut isapplying an axial force to the second embodiment of the deformablefastening thread, in accordance with “FIG. 12” of Appendix A.

APPENDIX

Appendix A contains a research project prepared at the inventor'srequest.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed is a fastener 100 including a head end 102, a helical thread104, and a groove 106 formed in the thread 104, as shown by example inthe figures. The fastener 100 may resemble a bolt or a screw, or anyfastener member or element that has a helical thread, however thefastener 100 described herein includes a groove 106 (FIG. 2-3) formedtherein which is not found in typical fasteners. Details of the groove106 are described in more detail below. The fastener 100 may include ormay be composed of steel or carbon steel material or a combinationthereof. The length of the fastener 100 may be between three-quarters ofan inch (¾″) to one and one half inches (1½). The fastener 100 may be anexisting conventional fastener which is augmented with the groove 106being formed therein, or preferably a newly manufactured fastener thatincludes the groove 106 as a result of initial manufacture.

The fastener 100 may be tightened into a material, substrate, orreceiving structure 108 such as a nut (FIGS. 1 and 3) having an internalthread 105. It is to be understood that as described herein, “receivingstructure” may refer to any structure that may receive the fastener 100,such as an internally threaded fastening member (nut) or a material orsubstrate (e.g. a sheet of metal or piece of wood).

The groove 106 causes the thread 104 to deform when an appropriate forceis applied to the thread 104 to increase a loosening resistance (i.e. toprevent loosening) of the fastener 100 while the fastener 100 istightened into a receiving structure 108, as described in detail below(FIG. 2).

When received in an appropriate structure (e.g. receiving structure 108or a material), the fastener 100 may be tightened by applying atightening torque to the fastener 100, or to a head 110 of the fastener100 (e.g. via a screwdriver or a wrench), to cause the fastener 100 torotate about a longitudinal or central axis of the fastener 100 orthread 104 and be axially displaced toward the receiving structure 108due to the applied rotation, causing the thread 104 to corkscrew intothe receiving structure 108. As such, the thread 104 may be configuredto cause an axial force 112 (FIG. 2) to be applied to the fastener 100due to a rotation occurring between the fastener 100 and a targetmaterial or receiving structure 108 (e.g. nut) while the fastener 100 isreceived or mated in the receiving structure 108. A tightening rotationmay cause a tightening axial force 112 (e.g. forcing the head 110 of thefastener 100 and a receiving structure 108 together), and a looseningrotation may cause a loosening axial force (e.g. forcing the head 110 ofthe fastener and a receiving structure 108 apart). For example, thethread 104 may have a helical or corkscrew configuration externallywrapping around a longitudinal body (e.g. shank or shaft) of thefastener 100 such that, upon the thread 104 being received by thereceiving structure 108, via a tightening direction of rotation, thefastener 100 may be tightened into the receiving structure 108, and viaan opposite, loosening direction of rotation, the fastener 100 may beloosened from the receiving structure 108. As such, when subjected tothe tightening rotation, the head of the fastener 100 and a receivingstructure 108 move toward each other, or in other words, a distancebetween the head 110 of the fastener 100 and the receiving structure 108decreases due to the tightening rotation. On the other hand, whensubjected to a loosening rotation, the head of the fastener 100 and thereceiving structure 108 may move apart, or a distance between the headof the fastener 100 and the receiving structure 108 may increase due tothe loosening rotation.

When a receiving structure 108 and/or the fastener 100 are tightened toa maximally tightened state with respect to one another, furthertightening torque or tightening axial force is resisted. For example,the fastener 100 and/or the receiving structure 108 may be tightened toa maximally tightened state when the receiving structure 108 iscontacting the head 110 of the fastener 100 or when both the head 110and the receiving structure 108 are contacting a material sandwichedbetween the receiving structure 108 and the head 110 of the fastener100. When not in this maximally tightened state, a receiving structure108 and the fastener 100 may be axially displaced relatively easily dueto relative rotation between the fastener 100 and the receivingstructure 108, since a longitudinal resistive force may not be present.

For example, a material (e.g. a sheet of metal, not shown in thedrawings) may have a bore, the fastener thread 104 may pass through thebore, and the receiving structure 108 may be disposed on an oppositeside of the material with respect to the head 110 to receive thefastener thread 104 in an internal thread 105 of the receiving structure108. In this example, the head 110 and the receiving structure 108 maybe larger than the bore such that the head 110 and the receivingstructure 108 cannot pass through the bore, and where the dimensions ofthe bore keep the head 110 and the receiving structure 108 on oppositesides of the material. The receiving structure 108 and the fastener 100may be tightened to a maximally tightened state where the material,between the head 110 of the fastener 100 and the receiving structure108, resists any further tightening and attractive motion between thereceiving structure 108 and the head 110. In some cases, a fastener maybe tightened into a material without requiring such a bore, and thefastener 100 may drill into the material while fastening to thematerial, or one or more materials sandwiched therebetween.

In this maximally tightened state, any or all subsequent tighteningtorque applied to the fastener 100 or the receiving structure 108 willbe transferred into an axial force 112 applied mainly or majorly toand/or between the threads of the fastener 100 and/or the receivingstructure 108 (FIG. 2), since the axial tightening displacement ormotion of the receiving structure 108 and/or the head 110 is resisted.Such a maximally tightened state occurs at a point where a tighteningtorque, and subsequently, an axial displacement, is longitudinally (i.e.axially) resisted to cause an axial force 112 to be directed to thethread 104 of the fastener 100 due to a tightening rotation, since ifthe longitudinal displacement of the fastening members is resisted, thehelical thread 104 would be subject to (i.e. absorb) an axial force 112directly in response to further applied tightening torque. For example,such an axial force 112 may be applied by an internal thread 105 of anut to an external thread 104 of a bolt in a maximally tightened state.As such, in this maximally tightened state, tightening torque istransferred to an axial force 112 majorly applied to the thread 104since the fastening members would be unable to longitudinally displace.Any situation or state where the axial displacement of the receivingstructure 108 or the fastener 100 is longitudinally or axially resistedmay be considered an appropriate maximally tightened state.

The present disclosure includes a groove 106 in the fastener thread 104to take advantage of such axial force 112 applied to the thread 104 andto provide loosening resistance of a threaded fastening arrangement. Forexample, the threaded fastening arrangement may be an arrangement wherea fastener 100 is tightenable into a receiving structure 108 orreceiving material.

The following terms and plain meanings and definitions thereof will beused to describe the disclosed fastener thread, the groove, and methodof using the same.

A major diameter of a fastener or thread is a diameter of an overallshaft of the fastener, including a height of a raised helix. A majordiameter may be measured on crests with a caliper ruler or slot gauge.For example, a major diameter of a thread may be a diameter of animaginary co-axial cylinder that just touches a crest of an externalthread. In other words, a major diameter may be a largest diameter of athread.

A minor diameter refers to or measures a diameter of a root or aninnermost part of a fastener thread and/or shank, not including crestsof a helix of the thread. For accuracy, this measurement requiresspecialized equipment. The minor diameter may be the diameter of animaginary cylinder that just touches roots of an external thread. As anon-limiting example, the minor diameter may be a diameter of animaginary cylinder that just touches crests of an internal thread, forexample, when the external thread is received in the internal thread. Inother words, the minor diameter is a smallest diameter of a shank orthread.

A pitch of a thread or fastener is a distance between two correspondingpoints on adjacent identical threads (i.e. between two identical,adjacent, thread “teeth” when viewed in longitudinal cross-section). Thepitch is analogous to a “period” in discussing wave phenomenon, suchthat the two points defining the length of the pitch are located atadjacent repeating points on the thread structure. The pitch of a threadmay be a distance, measured parallel to its axis, between correspondingpoints on adjacent repeating, identical, surfaces, in a same axial plane(e.g. where the points are co-linear with a line that is parallel with alongitudinal axis of the fastener shank). In other words, the pitch maybe a distance from a point on a fastener thread to a corresponding pointon a next thread.

A flank of a fastener or thread is a side at which a helix is raised toform a crest on the thread. The flanks of a thread are straight sidesthat connect a crest and a root. In other words, a flank may be asurface between a crest and an adjacent root, or may be a side of athread surface connecting a crest and a root.

A crest of a fastener or thread is a height at which an external threadis raised, or a depth at which an internal thread is indented (inembodiments where an internal thread and an external thread mate). Forcommon applications, fasteners such as screws and bolts are measured atcrests, while nuts or receiving members are measured at roots. Forexample, a crest of a thread is a prominent part of a thread, whetherinternal or external. A top surface with respect to a central axis of afastener may be considered a crest of a thread. In other words, a crestmay be a top surface joining two flanks or sides.

A root of a fastener is a bottom of a space between two flankingsurfaces of a thread whether internal or external. For example, a rootmay be considered a bottom surface joining two adjacent flanks of athread.

A pitch diameter, often called an effective diameter, is a diameter ofan imaginary co-axial cylinder which intersects a surface of a thread insuch a manner that an intercept of the cylinder, between points wherethe cylinder meets opposite flanks of a thread “tooth” (e.g. oppositeflanks sharing a crest), is equal to half a pitch of the thread. Forexample, the pitch diameter may be a diameter at which a line cuts thespaces between threads and threads equally, usually approximately halfway between the major and minor diameters. In other words, it measureshalfway up a helix crest. For accuracy, this measurement also requiresspecialized equipment.

The angle of a thread may be an angle between flanks, measured in anaxial plane section. In other words, the angle of a thread may be anangle between adjacent threads, where a root is or includes a vertex ofthe angle.

A longitudinal axis of a fastener is a longitudinal centerline of ashank or thread of the fastener. For example, the axis may besubstantially parallel and co-linear with a rotational axis on which thefastener rotates due to an applied tightening rotation.

A lead of a thread is an axial advance of a helix or screw during onecomplete turn (360°). For example, the lead for a fastener thread is theaxial travel resulting from a single revolution of the thread in areceiving member.

A tooth of a thread is a protruding part of the thread between twoadjacent roots of the thread, which is viewed in longitudinalcross-section along an axial plane.

The disclosed thread 104 may have an insertion direction flank 114facing away from the head end 102 and a removal direction flank 116facing towards the head end 102 (FIG. 2).

The removal direction flank 116 may have a groove 106 formed therein.The groove 106 may have a maximum depth being at least one half athickness of the helical thread 104 at a height position 118 of themaximum depth of the groove 106 on the helical thread 104. For example,the height position 118 may be a maximum point, apex, or peak of thegroove 106 with respect to a distance between roots 120 of the thread,or a distance between two adjacent lowest points (roots) of the threador thread tooth. For example, in longitudinal cross-section (FIG. 2),the thread may have a tooth 130 having first and second adjacent flanksthat meet at a single crest 122, where one of the flanks has the groove(e.g. removal direction flank 116) and subtends (e.g. imaginarily) tocontact or meet a minor diameter of the thread 104 at a first root point124, and where the other one of the flanks (e.g. insertion directionflank 114) may extend to meet or contact the minor diameter at a secondroot point 126, where the groove 106 may be disposed between the tworoot points 124 and 126. For example, the height position 118 may be atleast below a crest 122 of the thread such that a perpendicular lineextending from, and with respect to, the longitudinal axis of thefastener thread intersects the groove 106, the maximum depth, and/or theheight position 118 of the groove 106. The maximum depth of the groove106 may have a height dimension that is at least half a distance betweentwo adjacent roots 120, or half a distance between between the abovedescribed first root point and second root point, of the thread. In someembodiments, the maximum depth may be at least half a value of a pitchdistance of the thread. An exemplary preferred dimension or depth of thegroove may be between 50-55% of a distance between the above describedfirst and second root points.

As such, the groove 106 may be disposed at a root 120 of the thread 104.For example, the groove 106 may be disposed at a root 120 of the thread104 such that a surface of the root is co-planar or continuous (e.g. incross section) with a bottom surface of the groove 106. The groove 106may have a substantially triangular cross-section. In some embodiments,the groove 106 has a curve in its cross section (FIG. 3), the curvebeing between the height position 118 of the groove 106 and the removaldirection flank 116. In embodiments where the groove 106 is triangular,a surface of the groove 106 between the height position 118 of thegroove 106 and the removal direction flank 116 may be substantially flat(in longitudinal cross section), and a bottom surface of the groove 106may also be substantially flat (in longitudinal cross section), toproduce the triangular cross-section. For example, the triangular crosssection may have a first triangle vertex at a maximum depth (e.g. heightposition 118) of the groove 106, a second vertex where the groove meetsthe removal direction flank 116 surface, and a third vertex where asubtending line of the removal direction flank 116 surface meets a minordiameter of the thread or the shank of the fastener 100. The groove 106may be disposed substantially below a pitch diameter of the thread 104.

The groove 106 may be configured to allow the thread 104 to deform (FIG.2) and increase a major diameter of the thread 104 due to an axial force112. For example, the groove 106 may allow the thread 104 to plasticallydeform due to the axial force 112. As such, the groove 106 may bedimensioned specifically to allow this plastic deformation in responseto an appropriate tightening axial force 112, such as when the thread104 is subjected to a tightening axial force 112 when the fastenerand/or a receiving structure 108 are at a maximally tightened state asdescribed above. In other words, the groove 106 may allow the thread 104to plastically deform at a plastic hinge 128 near the root 120 of thethread 104. As such, a longitudinal “tooth” cross-section (e.g. tooth130) of the thread 104 may rotate about a plastic hinge due to thegroove's shape and an appropriate tightening axial force 112 to cause acrest 122 of the thread tooth 130 to extend laterally with respect to alongitudinal axis of the fastener thread 104 (e.g. the longitudinal axismay extend from the head end to a distal insertion end), and to causethe cross section of the groove to expand. For example, the axial force112 may be applied to the removal direction flank 116. The thread 104may deform at least to a plastic phase of deformation. One or more teeth130 near the head end 102 may deform. For example, at least 1-6 teeth130 near the head end 102 may be configured to deform as describedherein. In some embodiments, any tooth 130, any number of turns of thethread 104, or any portion of the thread 104 that is subjected to anappropriate axial force 112 may deform as described herein.

The axial force 112 may be applied in response to a tightening torqueapplied to the fastener 100. Due to the groove 106, the tighteningtorque may subsequently transfer to the thread 104 to cause adeformation of the thread 104 and to increase a major diameter of thethread 104 due to the deformation. For example, the tightening torquemay be applied when the fastener 100 and/or receiving structure 108 isat a maximally tightened state. The axial force 112 may be applied inresponse to a tightening torque applied to the fastener 100, thetightening torque causing the fastener 100 and a receiving structure 108to tighten together due to the thread 104 being helical. Due to thegroove 106, the tightening torque may transfer to cause a deformation ofthe thread 104 to increase the major diameter of the thread 104 due tothe deformation, the deformation being caused when a threshold axialforce 112 is applied to the removal direction flank 116. For example,the threshold axial force 112 may be determined by dimensions of thegroove 106, the external thread 104, and/or an internal thread 105 of areceiving structure 108. For example, a lead, pitch, or any of thedefined structures above, of a thread, may be specifically configured tocause the threshold tightening axial force 112 to be applied to thethread 104 for deforming the thread 104 as described herein. Specificdimensional and material characteristics of the thread 104 or areceiving structure 108 may determine an appropriate threshold axialforce 112. Further, dimensional tolerances between fastening members,threads, or receiving members may be selected to allow tightening torqueto be applied appropriately for being transferred into an axial forcethat deforms the thread as described herein.

The thread may deform to cause a crest 122, or a tip of the thread, toextend into a receiving structure 108 or an internally threaded member(FIG. 2). For example, the thread 104 may deform laterally due to thegroove to laterally cut into a root 121 of an internally threadedmember, receiving structure 108, or substrate. In other words,longitudinal forces such as an axial force 112 may be transferred to thethread to deform the thread, thus causing the axial force 112 totransfer into opposing transverse forces applied to a receivingstructure 108. For example, the opposing transverse forces may beapplied to a root 121 of an internally threaded structure like a nut dueto the deformation. For example, in FIG. 2, at t=1 an internal thread105 and an external thread 104 of the fastener 100 are being broughttogether, at t=2 the internal thread 105 and the external thread 104make contact at a removal direction flank 116 of the external thread104, at t=3 the axial force 112 starts to cause the external thread 104to deform toward the insertion direction flank 114, and at t=4 thethread 104 has deformed such that a crest 122 of the thread contacts andlaterally pushes on a root 121 of the internal thread 105 to produce aloosening resistance for the fastener 100. The dashed line in FIG. 2represents a previous, un-deformed, position of the thread.

The deformation of the thread may cause a wedge effect between one ormore crests of the thread and respectively mated roots of an internallythreaded structure (nut) or a receiving structure (FIG. 2), as thecrests of the thread 104 wedge into the receiving structure 108.Therefore, as an axial force 112 causes the deformation of the thread104, the axial force 112 transfers to a radial force applied outwardtoward a receiving structure 108 thus centrally compressing a base ofthe thread 104 (e.g. near the roots or the minor diameter) with at leastan intention of increasing the fastener's resistance to pull-out. Forexample, the crests of the thread may deform and become jammed into aninternal thread such that lateral displacement and loosening rotation isresisted due to the pressure exerted by the crests. Further, thesubsequent wedge effect may provide an increased tensile strength of thefastener, since upon applying the wedge effect, the wedge effectcompresses the thread toward a central axis of the thread.

As a further consequence of the groove in the thread, a typical failuremode observed in Appendix A moves to the deformable thread. For example,a first failure mode of a conventional fastener (excluding the groove)has been observed in Appendix A to be located near a root of a threadand a head of the fastener. This first failure mode shifts or moves tothe threads, since the threads are configured to deform due to anappropriate axial force, and hence absorb forces that are conventionallydirected to the first failure mode. This novel shift of failure mode tothe threads may have an advantage in real-world applications where thefirst failure mode is frequently observed to cause problems. Forexample, FIG. 4 shows an unstressed conventional fastener, and FIG. 5shows a typical failure mode (concentrated stress contours 402) of aconventional fastener, and FIG. 6 shows concentrated stress contours 602of the herein disclosed improved fastener thread 104. In comparison, itcan be seen that stress contours in FIG. 5 are concentrated near acorner 402 where the head and the root of the conventional screw threadmeet. As an improvement, it can be seen that the stress contours 602 inFIG. 6 are focused at the threads instead of being focused at thehead-root corner at 402.

In conclusion, disclosed is a novel and improved fastener thread thatprovides a loosening resistance due to a groove formed in the thread.

I claim:
 1. A fastener comprising: a head end; and a helical threadhaving a crest, an insertion direction flank facing away from said headend and a removal direction flank facing towards said head end, saidremoval direction flank having a groove formed therein, said groovehaving a depth allowing said thread to plastically deform at a plastichinge near said root of said thread for increasing a major diameter ofsaid thread due to an axial force.
 2. A fastener comprising: a head end;a helical thread having an insertion direction flank facing away fromsaid head end and a removal direction flank facing towards said headend, said removal direction flank having a groove formed therein; saidgroove being disposed at a root of said thread; said groove beingdisposed substantially below a pitch diameter of said thread; and saidgroove being configured for allowing said thread to deform and increasea major diameter of said thread due to an axial force.